Sunlight control materials, such as treated glass sheets, are commonly used for building glass windows and vehicle windows. Such materials typically offer high visible transmission and low emissivity thereby allowing more sunlight to pass through the glass window while block infrared (IR) radiation to reduce undesirable interior heating. In low emissivity (low-E) materials, IR radiation is mostly reflected with minimum absorption and emission, thus reducing the heat transferring to and from the low emissivity surface. Low-E panels are often formed by depositing a reflective layer (e.g., silver) onto a substrate, such as glass. The overall quality of the reflective layer is important for achieving the desired performance. In order to provide adhesion, as well as protection, several other layers are typically formed both under and over the reflective layer. These layers typically include dielectric layers, such as silicon nitride, tin oxide, and zinc oxide, which protect the stack from both the substrate and the environment. The dielectric layers may also act as optical fillers and function as anti-reflective coating layers to improve the optical characteristics of the panel.
A typical approach to reduce emissivity involves increasing the thickness of the reflective layer (e.g., the silver layer). However, as the thickness of the reflective layer increases, the visible light transmission of this layer is also reduced. Furthermore, the high thickness slows manufacturing throughput and increases costs. It may be desirable to keep the reflective layer as thin as possible, while still providing emissivity suitable for low-e applications.